12 HOWTO for multiqueue network device support
3 ===========================================
45 Section 1: Base driver requirements for implementing multiqueue support
67 Intro: Kernel support for multiqueue devices
8 ---------------------------------------------------------
910 Kernel support for multiqueue devices is always present.
1112 Section 1: Base driver requirements for implementing multiqueue support
13 -----------------------------------------------------------------------
1415 Base drivers are required to use the new alloc_etherdev_mq() or
16 alloc_netdev_mq() functions to allocate the subqueues for the device. The
17 underlying kernel API will take care of the allocation and deallocation of
18 the subqueue memory, as well as netdev configuration of where the queues
19 exist in memory.
2021 The base driver will also need to manage the queues as it does the global
22 netdev->queue_lock today. Therefore base drivers should use the
23 netif_{start|stop|wake}_subqueue() functions to manage each queue while the
24 device is still operational. netdev->queue_lock is still used when the device
25 comes online or when it's completely shut down (unregister_netdev(), etc.).
262728 Section 2: Qdisc support for multiqueue devices
2930 -----------------------------------------------
3132 Currently two qdiscs are optimized for multiqueue devices. The first is the
33 default pfifo_fast qdisc. This qdisc supports one qdisc per hardware queue.
34 A new round-robin qdisc, sch_multiq also supports multiple hardware queues. The
35 qdisc is responsible for classifying the skb's and then directing the skb's to
36 bands and queues based on the value in skb->queue_mapping. Use this field in
37 the base driver to determine which queue to send the skb to.
3839 sch_multiq has been added for hardware that wishes to avoid head-of-line
40 blocking. It will cycle though the bands and verify that the hardware queue
41 associated with the band is not stopped prior to dequeuing a packet.
4243 On qdisc load, the number of bands is based on the number of queues on the
44 hardware. Once the association is made, any skb with skb->queue_mapping set,
45 will be queued to the band associated with the hardware queue.
464748 Section 3: Brief howto using MULTIQ for multiqueue devices
49 ---------------------------------------------------------------
5051 The userspace command 'tc,' part of the iproute2 package, is used to configure
52 qdiscs. To add the MULTIQ qdisc to your network device, assuming the device
53 is called eth0, run the following command:
5455 # tc qdisc add dev eth0 root handle 1: multiq
5657 The qdisc will allocate the number of bands to equal the number of queues that
58 the device reports, and bring the qdisc online. Assuming eth0 has 4 Tx
59 queues, the band mapping would look like:
6061 band 0 => queue 0
62 band 1 => queue 1
63 band 2 => queue 2
64 band 3 => queue 3
6566 Traffic will begin flowing through each queue based on either the simple_tx_hash
67 function or based on netdev->select_queue() if you have it defined.
6869 The behavior of tc filters remains the same. However a new tc action,
70 skbedit, has been added. Assuming you wanted to route all traffic to a
71 specific host, for example 192.168.0.3, through a specific queue you could use
72 this action and establish a filter such as:
7374 tc filter add dev eth0 parent 1: protocol ip prio 1 u32 \
75 match ip dst 192.168.0.3 \
76 action skbedit queue_mapping 3
7778 Author: Alexander Duyck <alexander.h.duyck@intel.com>79 Original Author: Peter P. Waskiewicz Jr. <peter.p.waskiewicz.jr@intel.com>

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